There are four levels of reading, and most people stop at the second

Adler and Van Doren define four increasingly demanding levels: elementary reading (basic literacy — decoding words), inspectional reading (getting the gist of a book quickly, skimming for structure and main claims), analytical reading (thoroughly digesting a book — its terms, arguments, and structure — with unlimited time), and syntopical reading (comparing multiple books on the same topic against each other).

Their claim is that formal schooling gets most people reliably through the first two levels and rarely teaches the third or fourth explicitly, leaving most adult readers stuck extracting surface information from books that were written to reward much deeper engagement.

Each level includes the ones below it — you can't skip to analytical reading without first being able to inspect quickly, and syntopical reading requires solid analytical skill across several books at once. Takeaway: know which level a given book deserves, and don't mistake fast reading for real comprehension.